The invention relates to a motor vehicle having an underbody trim in the rear-end region of the motor vehicle, wherein the underbody trim is arranged below a floor panel of the motor vehicle and at least partially conceals a rear exhaust muffler.
A motor vehicle known, for example, from DE 43 19 281 A1 has a plate-like trim part below the floor panel. The trim part is provided with a multiplicity of air inlets. In this way, a boundary layer region, in which there is a risk of turbulence, at that side of the reinforcement part which faces toward the air flow while the motor vehicle is traveling is drawn away in the direction of the floor panel. The remaining part of the air at the flow-exposed side of the reinforcement part thus flows along the underbody trim in a laminar fashion, resulting in a lower air resistance. The known underbody trim also extends in the rear region of the motor vehicle and, here, conceals for example a fuel tank and a rear exhaust muffler.
It is an object of the invention to further develop the underbody trim of the known motor vehicle, in particular to obtain effective cooling of a rear exhaust muffler, without increasing the air resistance coefficient of the motor vehicle in the process.
This and other objects are achieved according to the invention by a motor vehicle having an underbody trim in the rear-end region of the motor vehicle, wherein the underbody trim is arranged below a floor panel of the motor vehicle and at least partially conceals a rear exhaust muffler. At least one air inlet is provided in the underbody trim, wherein the air inlet is provided in the region of the rear exhaust muffler, exclusively in a region in which, while the motor vehicle is traveling, a pressure is higher at the underside of the underbody trim than in an intermediate space between the underbody trim and the floor panel.
The core concept of the invention is that of providing the underbody trim with at least one air inlet in the region of the rear exhaust muffler, wherein the air inlet is arranged exclusively in a region in which, while the motor vehicle is traveling, a pressure is higher at the underside of the underbody trim panel than in the region of the floor panel situated thereabove. With an air inlet located in this way, it is achieved that the air flowing along the underbody trim flows into the air inlet solely on account of the pressure conditions between the outer side and the inner side of the underbody trim. In this way, a flow of ambient air into the intermediate space between the underbody trim and the floor panel is achieved with particularly low resistance, such that an adequate amount of cooling air is available for this region, which region is subjected to thermal load by the rear exhaust muffler. Owing to the fact that the cooling air flows in with low resistance, the air resistance coefficient of the motor vehicle is not increased, or is even reduced, in relation to a motor vehicle without the air inlet, such that in this way, despite improved thermal operational reliability of the motor vehicle, the fuel consumption thereof remains unchanged or is even lowered.
By performing pressure measurements in the rear-end region of motor vehicles, with a multiplicity of measurements at measurement points spaced apart from one another in the longitudinal direction of the motor vehicle, it is possible to localize a threshold point or a line of threshold points running approximately in the transverse direction of the motor vehicle. At said threshold point, or at said threshold points, the negative pressure at the underside of the underbody trim and the negative pressure in the intermediate space between underbody trim and floor panel are equal. As already explained above, while the motor vehicle is traveling, in the region behind said threshold point or behind said threshold points, it is possible for a fraction of the underbody flow to flow of its own accord into the intermediate space between underbody trim and floor panel owing to the pressure conditions. According to the invention, the air inlet is arranged, in a targeted fashion, in the region behind the threshold point or behind the line of threshold points.
The region that is subject to thermal load is primarily the surroundings of the rear exhaust muffler that is concealed by the underbody trim. The underbody trim prevents the thermal energy in this region from being able to escape by convection or radiation. As a result, without additional measures, there would be an inadmissibly high temperature in the surroundings of the rear exhaust muffler, and of the floor panel arranged above the rear exhaust muffler and possibly of components arranged above the floor panel in the luggage compartment. It is often the case that electrical and electronic components such as, for example, a starter battery or a control unit are arranged in the lower region of the luggage compartment. Furthermore, components of chassis control systems are often also situated in the surroundings of the rear exhaust muffler.
As a result of the introduction, according to the invention, of cooling air with low resistance into regions subject to relatively high thermal load (so-called “hotspots”), the thermal operational reliability of the motor vehicle is improved. By means of an air inlet according to the invention, the temperature at the floor panel of the motor vehicle can be minimized. The invention can be used in all variants of motor vehicles, regardless of the drive, engine and/or bodyshell concept. The phenomenon of the pressure being higher in a particular region under the underbody trim than in the intermediate space, situated thereabove, between the underbody trim and floor panel arises even at low speeds, and is intensified with increasing speed of the motor vehicle, such that the invention is highly effective in many operating states of the motor vehicle.
The at least one air inlet may be designed in any desired way, for example as a classic ramp, as a large NACA inlet, in the form of multiple small NACA inlets, etc. If multiple inlets are provided, these are arranged adjacent to one another as viewed in the direction of travel, that is to say arranged in the transverse direction of the motor vehicle, at least approximately in a row.
In one advantageous refinement of the invention, the underbody trim is formed in the manner of a diffuser, with a level of the underbody trim rising in the vertical direction of the motor vehicle counter to the direction of travel. Owing to the fact that the spacing between the underside of the underbody trim and the roadway increases toward the rear-end region of the motor vehicle, the pressure at the underside of the underbody trim increases continuously, or in other words the negative pressure at the underbody trim decreases, in the direction of the rear end of the vehicle during forward travel of the motor vehicle. Furthermore, the design of the underbody trim as a diffuser has an advantageous effect on the left of the motor vehicle, and thus on the driving characteristics of the motor vehicle.
The invention can be realized in two basic embodiments depending on the structural height of the rear exhaust muffler.
In the case of motor vehicles with a rear exhaust muffler which, owing to its structural height, is situated in the intermediate space between the floor panel and the underbody trim, and which can thus be completely concealed by the underbody trim, the air inlet is formed exclusively by a cutout in the underbody trim. Said cutout is, as viewed in the vertical direction of the motor vehicle, arranged below the underside of the rear exhaust muffler. Here, the position term “below” relates to the vertical direction of the motor vehicle and does not exclude an offset in the longitudinal direction of the motor vehicle.
In the case of motor vehicles with a rear exhaust muffler which, owing to its structural height, cannot be completely concealed by underbody trim, the underbody trim has a cutout which is larger than the air inlet. It is thus possible for the underside of the rear exhaust muffler to project through the cutout in the underbody trim, that is to say the underside of the rear exhaust muffler protrudes downward beyond the contour of the underbody trim. Here, the front edge of the cutout adjoins the front side of the rear exhaust muffler, which protrudes downwardly in the direction of the roadway, with the smallest possible gap. This region is designed such that the air flowing along the underbody flows over the gap with the least possible losses. By contrast, at the rear side of the rear exhaust muffler, a relatively large gap is intentionally provided between the rear exhaust muffler and the rear edge of the cutout. This gap constitutes the air inlet, that is to say the rear exhaust muffler forms the air inlet in interaction with the cutout in the underbody trim.
The invention can advantageously be used in motor vehicles which have a rear exhaust muffler arranged transversely with respect to the direction of travel. The invention can, however, basically also be used in motor vehicles which have a rear exhaust muffler arranged obliquely with respect to the direction of travel or in the direction of travel.
In a preferred refinement of the invention, the air inlet is arranged behind the rear exhaust muffler as viewed in the longitudinal direction of the motor vehicle. It is achieved in this way that the air flows into the intermediate space between the floor panel and the underbody trim behind the rear exhaust muffler and, after being diverted into the direction of travel, can flow around the entire rear exhaust muffler.
In a further refinement of the invention, at least one air-guiding panel is provided by which the air that flows upward in the direction of the floor panel from the underbody flow is guided around the rear exhaust muffler. The air-guiding panel can interact with a heat shield panel, which shields the heat radiation from the rear exhaust muffler, by virtue of said heat shield panel additionally performing air-guiding tasks. It is likewise possible for the air-guiding panel to perform the function of a heat shield panel. The combination of air-guiding panel and heat shield plate thus ensures an effective flow of cooling ambient air around the rear exhaust muffler and, if appropriate, adjacent regions.
The underbody trim according to the invention covers as large a part of the underbody of the motor vehicle as possible in order that flow passes around the latter with low flow losses. In a first embodiment of the invention, the underbody trim begins directly after the rear axle and extends as far as the trim of the rear bumper. Here, the underbody trim adjoins the trim of the rear bumper, and adjacent components if appropriate, in an aerodynamically expedient manner, as far as possible without steps and joints. In a second embodiment of the invention, the underbody trim even begins in front of the rear axle and thus additionally covers the region of the rear axle, resulting in further improved aerodynamic effectiveness which results firstly from the optimized flow over the rear axle and secondly from the greater “approach” provided for the flow for a uniform flow around the rear-end region of the motor vehicle.
As well as concealing the rear exhaust muffler and, if appropriate, the region of the rear axle, the underbody trim also conceals a section of greater or lesser length of the pipeline, which leads to the rear exhaust muffler, of the exhaust system of the motor vehicle. The fuel tank of the motor vehicle is advantageously also concealed by the underbody trim.
The underbody trim is mounted on the motor vehicle by means of conventional connecting technologies such as screws, clips, welding, adhesive bonding, etc. The material of the underbody trim should be selected in accordance with the specific requirements (strengths, stiffness, heat resistance, flexibility, etc.). The underbody trim will be provided in part, or over the full area, with reinforcements, coatings and the like in accordance with the prevailing loads.
The position terms “front”, “rear”, “top”, “bottom”, “inside”, “outside”, etc. used in conjunction with the present invention relate to the installation position of the respective components in the motor vehicle during forward travel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.